Baked-film resistors basically consist of a resistance film formed on an insulating substrate by baking the resistance paste. As a material for producing such resistance films, it has been proposed in various patent specifications and literature to use resistance paste containing, as a conducting component, metal oxides. For example, Japanese patent publication Nos. 27871/1976 and 28162/1980 disclose resistance paste containing Bi.sub.2 O.sub.3 -RuO.sub.2 or Pb.sub.3 O.sub.4 -RuO.sub.2 as the conducting component. When manufacturing resistors, such resistance paste is applied by screen printing to an insulating substrate such as, for example, an alumina substrate, and baked in air to form a resistance film.
Such a resistance film exhibits a good stability of resistance with voltage, temperature and humidity, but it is poor in resistance to wear caused by sliding contact with a slider, which is mounted on a shaft concentric with a ring having the resistance film thereon. Thus, adjustable film resistors containing metal oxides as a conducting material have a serious wear problem awaiting a solution. For example, their resitance changes by 30 to 50% with respect to its initial value after only 100 times of rotation of the slider. In addition, the resistance paste of the prior art contains a large amount of expensive ruthenium. For example, the resistance paste of the Bi.sub.2 O.sub.3 -RuO.sub.2 system contains RuO.sub.2 such that a molar ratio of Bi to Ru is 4:5 to 4:8. Thus, it is difficult to cut down the manufacturing cost of the resistors. In the Pb.sub.3 O.sub.4 -RuO.sub.2 system, a molar ratio of PbO to RuO.sub.2 is 1:1 to 2:1.